FR2492173A1 - ELECTRONIC ELEMENT AND ANODE FOR ELECTROCHEMICAL ELEMENT - Google Patents

Abstract

THE PRESENT INVENTION CONCERNS AN ELECTROCHEMICAL ELEMENT 10 INCLUDING AN ANODE 16 BASED ON AN ELECTROPOSITIVE ELECTRONICALLY CONDUCTIVE SUBSTANCE WHICH IS IN A MELT STATE AT THE TEMPERATURE OF THE ELEMENT'S OPERATION, A COMPATIBLE ELECTROLYTE 20 AND A COMPATIBLE CATHODE 20. ACCORDING TO THE 'INVENTION THE ELEMENT INCLUDES FURTHER A MICROMOLECULAR SIEVE SUPPORT 18 SENSITIVELY NON-ELECTRONICALLY CONDUCTIVE IN WHICH THE ELECTROPOSITIVE SUBSTANCE IS ABSORBED AND MAINTAINED IN A DISPERSE FORM, THE MICROMOLECULAR SIEVE SUPPORT BEING SEALED BETWEEN THE LIQUID AND THE LIQUID AND THE PLATE CATHODE OF THE ELECTROPOSITIVE SUBSTANCE OF THE ANODE. THE ELECTROCHEMICAL ELEMENT CAN BE USED IN PARTICULAR IN ACCUMULATORS.

Description

Electrochemical element and anode for electrochemical element.

  The present invention relates to an electrochemical element and an anode structure for such an electrochemical element.

  used in an accumulator (ie a recharging element

  geable). Recently, increased attention has been given to the development of

  means for storing energy.

  However, these developments have been delayed to some degree

  different from the difficulties encountered in effectively controlling

  electrochemically mobile active substances and by the difficulties encountered in operating at high temperatures, temperatures which in many cases are necessary for efficient operation of

electrochemical elements.

  According to one of its aspects, the subject of the present invention is an electrochemical element which comprises an anode which comprises, as electrochemically active anode material, an electronically conductive electro-positive substance which is in the molten state at the operating temperature of the element; a compatible electrolyte, and a compatible cathode,

  the element further comprising a micromolecular sieve support

  a substantially electronically non-conductive film in which the electropositive substance is absorbed and is kept in dispersed form, the micromolecular sieve support being liquid-tight and positioned between and separating the electrolyte and the cathode from the electropositive substance

lOde the anode * -

  Liquid-tight means that all electrochemically active substances when they go from the anode to the cathode or vice versa must pass through the

  internal pore (cavity structure of the support).

  According to another aspect, the subject of the present invention is a composite anode structure constituted by

  an x encromolecular sieve support substantially

  electronically conducting in which the anode material

  electrochemically active in the form of an

  electronically conductive tropositive is absorbed and maintained in dispersed form and a reservoir or source of electropositive material in contact with the support, for use with a compatible electrolyte and cathode in an electrochemical element in which the electropositive substance of the reservoir is in the state Fused without being bound by theory, Applicant believes that the electropositive substance can form electronically conductive passages extending along at least some of the channels and / or pores in the body. support, which puts at least some of the windows in the surface of the support in electronic contact with each other by the interior of the support. During use, these passages can thus act to make the support, when doped with the electropositive substance, electronically conducting as a whole, through the passages so that the electrons can circulate along the passages, the interface between the support and the electrolyte, towards the interface between the support and the electropositive substance of the anode. The applicant believes that it is possible that the electropositive substance is absorbed in elemental form,

  the electropositive substance being kept in the form of

  persried in the support and being mobile in the form of an atom or in elemental form along the channels and / or pores of the support to occupy suitable locations left free by other atoms of the electropositive substance, so that it can be move during use

  from the anode to the electrolyte through the support.

  When there is a danger, as in the case where the electrolyte is liquid at the operating temperature of the element, that the electropositive substance can chemically react undesirably with the electrolyte, for example with the anions of the electrolyte. the carrier, when it contains the absorbed electropositive substance, may be selected or modified so that the windows in its microporous inward surface prevent sufficient access to

  the interior of the support, for example anions of the electro-

  lyte for the unwanted reaction to take place. Moreover, when, as described hereinafter, the electrolyte chosen is

  an aqueous solution, the support, when it contains the sub-

  electropositive stance absorbed, can be chosen or modified

  so that the windows or pores in its surface do not allow

  do not put inward access to the water molecules.

  The substance. electropositive will be in the molten state at the

  operating temperature of the element and may include

  or consist of an alkali metal or an alkali metal

  earthy, a combination or an alloy of two or more alkali or alkaline earth metals or a combination or

  alloy of one or more alkali metals or alkaline earth metals

  earthy with one or more other substances. In other words, the alkali metal or alkaline earth metal or metals may be used alone or in combination of two or more thereof or one, two or more of said metals may be used in the form of a compound. - an alloy or an alloy with one or more other compatible substances provided that they are such that the electropositive substance is in a molten state at a temperature of

operation of the element.

  The alkali metal (s) of the electropositive substance may be in any suitable combination containing, for example, lithium, sodium, and / or potassium. The alkaline earth metals may similarly be under any suitable combination of alkaline earth metals

  such as calcium or magnesium. The electro substance--

  positive, as mentioned above, is in the molten state at the operating temperature of the element. For use at atmospheric pressure, certain sodium or potassium alloys are particularly suitable because they have melting points below 1000C and potassium and in particular sodium can be used alone because of their commercial availability.

at competitive prices.

  By "micromolecular sieve support" is meant a molecular sieve support having internally interconnected cavities and / or channels and, in its surface, windows and / or pores leading to said cavities and channels, the windows, pores, cavities and / or channels having a dimension of less than 50 Angstroms and preferably less than 20 Angstroms or when it is intended to be used with an electrolyte constituted by an aqueous solution, such that the water molecules can not not be absorbed inside the support, irrespective of the fact that other substances

  absorbed are present or not in the cavities of the support.

  Suitable micromolecular sieves are inorganic micromolecular sieve carriers, ie, lattice or backbone mineral structures, although some essentially organic micromolecular sieve carriers such as clathrates may, under certain circumstances, be suitable as mentioned below. Suitable micromolecular sieve supports may be selected from the group consisting of tectosilicates, ie the class of substances also known as "skeleton silicates" which may be

  natural or synthetic, crystalline or non-crystalline

  These include silicates, for example silica gel, zeolites, feldspars and feldsparents, which are silicates having a type of structure in which the four oxygen atoms of the silicate tetrahedron are

  p artages with neighboring lestrahedrons. The skeleton of the tecto-

  silicate is composed of silicon atoms with in some

  case of aluminum atoms, together with other atoms.

  Micromolecular mineral sieves also comprise mixtures of or analogs of tectosilicates in which the silicon and / or aluminum atoms of the backbone may be substituted inter alia by atoms of one or more of the following elements: iron, beryllium , boron, phosphorus, carbon, germanium and gallium in small or large proportions and in which the characteristics and properties of the micromolecular sieving are not affected by the substitution. As long as the applicable properties for the present invention

  are not significantly affected, these analogues are

  as tectosilicates in the context of the

this description.

  Conveniently, for the molten salt electrolytes, the micromolecular sieve support is a zeolite or, where the electrolyte must be aqueous, the support may be a tectosilicate which can not absorb water, for example

a feldspar or a feldspatholde.

  Zeolites, feldspars and feldspathoids are found in the class of natural or synthetic, crystalline or amorphous materials which contain aluminum and silicon in well-defined proportions and their analogues. For a more detailed discussion of zeolites, reference may be made to the January 1975 publication of the International Union of Pure and Applied Chemistry entitled "Nomenclature

  chemical composition of synthetic zeolites

ticks and natural ".

  The zeolites contain absorbed water molecules which can be removed, usually reversibly, by heating and / or under vacuum. Although it is expected that the molecular sieve supports of zeolites that are

  at least partially dehydrated and usually

  dewatered water is generally used, the presence of water in the zeolite may, in some cases, be an advantage to increase the ionic conductivity depending on the mechanism

  reaction of the element as discussed below.

  Zeolites, feldspars and feldspar-

  a reasonably ordered internal structure, pre-

  feel a high internal surface and are characterized by

  the presence of multiple regular rows of molecular cavities

  culaires ie channels and / or cavities opening on the surface of the zeolite through windows and / or pores. Other tectosilicates, in particular amorphous

  or non-crystalline, have a sensi-

  less orderly or in fact unordered, even though

  while they keep suitable rows of small cavities

  léculaires. It is believed that zeolites in their hydrated form can be represented by the following structural formula: M2 / nO.Al2O3.Xsio2. YH20 in which M is a cation of valence n and X and Y are independent variables which are a function of composition

  of the starting material and its mode of formation.

  It has been found that suitable tectosilicate crystals can have a sufficiently high physical strength to be used effectively in the element of the present invention. (When the tectosilicate is in powder form, it can be compacted and supported, for example, in a

  porous container during use).

  In addition, it has been found that tectosilicate crystals that have been doped with an electropositive substance can withstand sufficiently the electrochemical and thermal damage resulting from repeated use in an element.

according to the present invention.

  When crystalline tectosilicates are used, a physical or electrochemical defect of the doped tectosilicates

  with electropositive substances will not be

  one of the factors that contributes significantly, if any, to a failure of the elements

according to the present invention.

  In the present invention the micromolecular sieve support is provided to have a three-dimensional backbone structure which remains physically and electrochemically stable, so that it does not deform significantly as a result of the electrochemical reaction during normal and continuous use. operate as a sieve for diffusion

  of the electropositive substance through it while preventing

  the access to the interior of the electropositive substance, anions of the electrolyte with which it is used, in cases where the anions react undesirably with the electropositive substance of the anode and prevent access

  water when the electrolyte is an aqueous solution.

  Thus, these aspects will be kept in mind when choosing the particular molecular sieve support for use with electropositive substances and electrolytes.

  chosen during the implementation of the present invention.

  It should be noted, however, that when certain supports are doped with highly electropositive substances such as lithium metal alone or in combination with other metals, a substantial change in the network structure of the support may result. It has been found, however, that such modified lattice structures still possess the necessary properties that they can act as a support and / or sieve for the electropositive material, are sufficiently inert electrochemically or relatively inert electrochemically during their use in

  an element and may prevent access to the electronic substance

  negative chemical substances or when

  is present, the access of water from the electrolyte.

  Such carriers, for example tectosilicates such as zeolites which have been physically and / or chemically modified during doping with the chosen electropositive substances but which still possess the necessary properties, can thus be usefully employed as a micromolecular sieve support. in the anodes of this

  invention, and in the sense of the present description these tecto-

  modified silicates, zeolites, etc. are still considered as tectosilicates, zeolites, etc. It should be noted moreover that, in the case of certain tectosilicates,

  an exchange of incident cations can occur during use

  use of the anodes according to the present invention in certain electrochemical elements. Such reactions are well known and mainly modify the dimensions of the windows and pores of the support network, and this aspect will be kept in mind when choosing the electropositive substance and the support to ensure that the pores or windows of the support have the same characteristics. desired dimensions to allow

  the passage of the electropositive substance through them while em-

  for the electrolyte water, when an aqueous electrolyte is used in the undesirable electrolyte elements and anions in cases where these anions are chemically unstable relative to the electropositive substances. AT

  again, these elements are still considered as tecto-

silicates of the type in question.

  Thus, it will be appreciated that although the tectosilicate molecular sieve carriers of the present invention may, in some cases, after doping or after being subjected to multiple charge / discharge cycles in an element, no longer be strictly in the form of tectosilicate as such in the usual sense, they can still be considered as such or at least as micronolecular micronolecular sieve supports in the context of the present invention, provided

  they have the required properties.

  Thus, when the tectosilicate molecular sieve shaped supports of the electrodes of the present invention are in the form of modified tectosilicates, they are such

  that, although physically or chemically modified, they possess

  The molecular cavities or pores suitable for receiving the electropositive substance, channels or pores which lead to the cavities, and windows of appropriate size are also suitable.

  Thus, when the molecular sieve supports of the pre-

  The present invention is in the form of modified substances, those having windows, channels, pores and cavities for receiving electropositive substances and for allowing the passage of electropositive substances.

  while excluding water and / or unwanted anions from the electri-

  trolyte. Taking into account factors such as pore size, channel size, cavity size and window size, as well as the ability to absorb substances

  electroposed in effective amounts, while allowing

  high mobility or passage of electro-

  positive through said carrier and excluding water and / or anions of the electrolyte which are unstable relative to the electropositive substances, an approximate guide can be obtained for the selection of suitable molecular sieve carriers for use in accordance with the present invention. Additional factors that may also serve as a guide may be the degree of porosity, density, availability and strength, stability and conductivity

  or lack thereof, micromolecular sieve supports

doped.

  For example, sodalite has good structural properties enabling it to function, as described hereinafter, as a molecular sieve support in accordance with the present invention.

  invention. Such aluminosilicates or the like which

  acceptable structural properties to function as required by the present invention may constitute

  tectosilicate molecular sieve supports suitable for

  ble. The micromolecular sieve support will preferably be such that the electropositive substance when absorbed into the support is kept in a finely dispersed elemental form, for example, if possible, in the form of an atom, a molecule, a set of 'atoms or a set of molecules

  to use during its use the widest available

  bility for electrochemical activity.

  In addition, the support will preferably be such that it keeps inside an effective amount of electropositive substance for electronic conduction, and if necessary ionic effective for the electropositive substance to move.

in effective amounts.

  In the present invention, it is believed that the media can

  in fact act as a sieve allowing a diffusion of substances

  these electropositive devices through the medium in

  ion, atom or ion from the anode to the electrolyte

  discharge of the element while preventing access to substances

  these electropositive contained inside the support, e and / or anions of the electrolyte if they are unstable compared to electropositive substances. During use, the function of the supports is thus to prevent a reduction of the electrolyte by the electropositive substances contained in the anode and to prevent a reaction of these electropositive substances with the water in the electrolyte. It is contemplated that the element of the present invention may, if desired, be used as an accumulator or rechargeable element and, during charging, the electropositive substances diffused

from the electrolyte to the anode.

  The anode structures of the present invention are particularly useful in electrochemical elements employing

  electrolytes based on liquid molten salt or electro-

  lytes in the form of an aqueous solution and intended to operate at relatively low temperatures, for example, of the order

  from room temperature to around 3600C.

  In such elements, the cathodes may comprise an oxide of one or more transition metals selected from, for example, the group consisting of manganese, iron

  and nickel or a hard refractory metal compound

  at least one metal selected from the group consisting of chromium, manganese, iron, cobalt and nickel with at least one non-metal selected from the group consisting of carbon, boron, nitrogen, silicon and phosphorus that have been activated by halogenation. Thus, for example, the cathode may comprise a hard refractory metal compound

  which is an activated carbide of iron, chromium or manganese.

  Instead, the cathode may include sulfur and / or selenium and a micromolecular sieve support, for example, a tectosilicate in which sulfur and / or selenium is absorbed and is held captive during use of the cathode in the process. 'element. The sulfur and / or selenium may for example be absorbed in a dehydrated zeolite molecular sieve support which may be selected from the group consisting of erionite, faujasite, synthetic zeolite 3A, zeolite 4A and zeolite 13X. The zeolite support material will be rendered electronically conductive by the addition of a suitable electron conducting material such as graphite. For such elements operating at low temperature, the electrolyte may be an acid or an aqueous base, for example

  an aqueous solution of sodium hydroxide, or hyaluronic acid,

  potassium hydroxide, or it may be based on a mineral salt

  melted such as an electrolyte of a mineral salt based on iodide.

  Thus, to test this possibility, the eutectic mixture of lithium iodide / potassium iodide was prepared in the ratio described by D. B Leiser and A. Whittemore Jr. J. Amer. Ceram. Soc. 50 (1961), 60. This mixture was doped with 99.5% pure strontium iodide obtained from Cerac Inc. The components were mixed and ground together as a fine powder and melted in tubes of

glass in a stream of argon.

  Temperatures were recorded for which the mixtures were melted and solidified. Solid mixtures

  homogenous materials were then crushed and the deter-

  exact melting point. The amount of sodium iodide added varied from about 25% to about 50% by weight of the mixture. Melting points were found to be in the range of 2201C to 2400C while the eutectic mixture of lithium iodide / iodide

  of potassium melted at about 2600C.

  Instead, the electrolyte may consist of an electrolyte

  molten mineral salt trolyte having the general formula: M Al Hal4 wherein M represents one or more alkali or alkaline earth metal cations and Hal represents one or more halogen atoms, the proportions of the alkali metal cations or of the alkaline earth metal and halogen anions are conveniently such that the above stoichiometric product is maintained, the alkali metal cations and the halogen anions being selected from

  electrolyte has a sufficient melting point

  low to allow use in its state

  melted at the desired operating temperature of the

is lying.

  When such an electrolyte is used with a tectosilicate support and when the electropositive substance of the anode (for example one or more alkali metals) is capable of reducing the aluminum of the electrolyte to cover it anode and / or to separate from the electrolyte for example to precipitate, the size of the windows or pores of the molecular sieve support of the anode will be such that

  the windows prevent the access of Al Hal41 anions from the elec-

  trolyte inward of the zeolite of the anode. When the halide ions are AlCl41 ions, the dimension

  windows or pores of the tectosilicate will be such as to

  This is largely the case with the passage of these anions, while it is difficult to facilitate. ent the access of the electropositive material, for example atoms or ions of lithium, sodium and / or potassium through the windows or pores to the inside of the zeolite. In this way, it is avoided that the Al Hal41- anions come into direct contact with the electropositive material in its elemental or atom / molecule form, so that a reduction and separation of aluminum by means of a counter-reaction can not easily and directly take place. The tectosilicate molecular sieve carriers which are suitable for use in conjunction with molten salt electrolytes of formula M Al Hal4 may be selected from the group consisting of sodalite,

  carnegieite, zeolite 4A, zeolite 13X and mordenite.

  In the case of aqueous electrolytes, their test as electro-

  lytes in elements according to the present invention

  having sodium / potassium anodes and cathodes

  taking manganese dioxide, promises to provide a

  Excellent electrochemical abortion at temperatures of

  operating below 100 C.

  When such electrolytes are used with a tectosilicate support, the electropositive substance of the anode (for example one or more alkali metals) is likely to react with the water of the electrolyte, so that the size of the windows or pores of the support in molecular sieve should be such that the windows prevent

  the access of the electrolyte water to the interior of the anode.

  The size of the windows or pores of the tectosilicate will be such that it largely elutes the passage of water while it allows easy access through the windows or pores inside the anode for the electropositive material, for example the atoms or ions of sodium, lithium and / or

of potassium.

  In this way, it is prevented that the water comes into direct contact with the electropositive material in its elemental or atomic / molecule form so that the reaction

undesired can not take place.

  Without wishing to be bound by theory, it is believed that in microscale sieve carriers which have cavities in the form of capillary channels or of the tubular type, which may have a dimension substantially equal to the size of the pores or windows, the electropositive substance may moving along the channels during the discharge of the source of the electropositive material at the interface between the support and the electrolyte and that, in some cases, the electropositive substance in the channels may maintain electronic contact with the electropositive substance reservoir through the body of the support. In other words, the support

  will be, in this case, electronically conductive through the electropositive substance in the channels, between the

  reservoir or source of the electropositive substance and the electrolyte. In this regard, it will be understood that the source of the electropositive substance is not in direct contact with the electrolyte except via the carrier.

micromolecular sieve doped.

  In the case where the doped molecular sieve support is electron conducting a possible mechanism is that during

  the discharge of the element, the atoms of the

  positively ionize at the interface between the electro-

  lyte and support in molecular sieves, and that the ions

  pass into the electrolyte, the electrons coming from the ioni-

  passing through the electropositive substance

  the interior of the support to said source of electropoly material

  which acts as or may be associated with a collection of

  current generator. At the same time, the atoms of the electropositive substance pass from the source of the anode material into the material of the molecular sieve support to replace those which have been ionized, a rapid diffusion of the electropositive material taking place through the channels of the molecular sieve support. from the anode to the electrolyte. According to this mechanism, the electropositive substance

  may be present in the form of electronic son or chains

  only conductors in the channels. However, it is pos-

  that in place of the electropositive material in the form of electronically conductive chains or wires in the channels, the electrochemically active atoms of the absorbed electronically conductive substance can form groups of particles with suitable cations forming part of the network or matrix of molecular sieve material. These groups can

  to associate with the electrons from the electro substance

  positive absorbed. Such electrons can be sufficiently

  moving through the molecular sieve support.

  -20 eyepiece of its interface with the electrolyte o takes place the ionization up to the anode tank and

there at the collector.

  If, however, the mechanism suggested above by which ionization takes place at the interface between the support in

  molecular sieve and the electrolyte is incorrect and if ionizing

  take place at the interface of the molecular sieve support.

  re and the anode or source of electropositive substance or if a hybrid mechanism exists by which source ionization is sufficiently predominant, then the molecular sieve support into which the electropositive substance has been absorbed can not, strictly speaking, operate as a sieve, but can instead function as a solid electrolyte. Ions instead of atoms will diffuse

  then quickly through the molecular sieve support.

  This process can be enhanced by the presence of the absorbed atoms in the form of groups of particles, the solid electrolyte being constituted by metal-rich groups, for example Na.sub.33 in a sodalite. However, whether the support impregnated with electropositive substance is considered as a sieve or a solid or non-solid electrolyte, this does not affect its usefulness and its function as described above in

  the anode elements and structures of the present invention

  vention. To prepare a carrier according to the present invention, a tectosilicate, for example a suitable feldspar or feldsparoid, or a zeolite which is wholly or partially

  dehydrated by subjecting it to vacuum and heat is

  se, optionally under pressure and after being

  vacuum, the vapor of the electronic substance

  positive that must be absorbed into it. Although it is not necessary to saturate all the free places in the zeolite molecular sieve support with the electropositive substance and only a desired proportion of free places need to be occupied, it is considered that

  practice to be absorbed into the molecular sieve

  zeolite rod as much as possible of electropositive material.

  The size of the pores or windows of the molecular sieve support

  The zeolite rod may or may not be modified by the absorption of the electropositive material, and the zeolite molecular sieve support will be chosen so that its channel and pore dimensions, in particular its windows are, after doping, such as

  works effectively to exclude any anion that is insta-

  relative to the alkali metal of the anode or the water

  electrolyte from the reaction with the electropositive material in the channels during use. In other words, if such a modification takes place, the micromolecular sieve support and the metals must be chosen so that the resulting molecular sieve support has channel, pore and

suitable windows.

  Thus lithium, sodium or potassium may be used alone or such alkali metals may be used together, or they may be used together with other metals such as, for example, aluminum. It is believed that when an electropositive substance such as sodium or lithium is used together with another metal such as aluminum, both the alkali metal and the other metal such as aluminum can be absorbed into the metal.

  the support, the other metal modifying the support

  zeolite rod by reducing the actual size of the channels, pores and / or windows to the desired appropriate value for the projected use of the anode. Thus, starting with a molecular sieve support that has channels, pores and in particular windows that are too wide to exclude unwanted ions from the electrolyte, after absorption of the other metal, the size of these channels, pores and / or windows can be reduced by the presence of the atoms of the other metal obstructing them, so they have

  the exact dimension to exclude water or ions from the electri-

  undesired trolyte, while allowing the passage or entry of atoms / ions of the electropositive alkali metal such as

  sodium, potassium and / or lithium.

  Consideration is also given to the possibility that when the

  pores of the support are sufficiently large, molecules

  the electrolyte may, at the initial stage of operation,

  element, to be able to penetrate

  part of the support body, at the point where a reaction

  occurs with the electropositive substance, the resulting products of which serve to reduce the size of the

  cavity which prevents further penetration of electricity

  trolyte and any additional reactions, so that the action of the element is that described above, for example when sodium is the electropositive material, the sodium aluminum chloride is the liquid electrolyte and the reaction causes a precipitation metallic aluminum

  which serves to block the cavities to the desired extent.

  It will thus be understood that either a suitable molecular sieve support may be chosen which initially has windows, pores and channels of correct size, or it may be chosen to have dimensions of this size.

  are too large and modify it during the absorption process.

  so that it ends with pores, channels and windows of appropriate size. In this case, the other metal such as aluminum or even nickel, which is used together with the electrochemically active electropositive alkali metal can form an effective coating on the channels, to remain there while being relatively electrochemically inert in the element by acting to reduce the dimensions of

  channels, pores and / or windows and also acting to increase

  Be the electronic conductivity along the passages formed by the channels containing electrochemically active electropositive substance. So some substances of the material

  absorbed can act to modify the molecular sieve support.

  to stabilize it while increasing its conductivity.

  electronic tivity along the passages formed by the channels while other substances can act as electropositive material. The electron conduction properties of the molecular sieve support can thus, it is believed, be limited to the channels while the body of the molecular sieve support or at least its part which is in direct contact with the liquid electrolyte, will be or little electron conductor to prevent the deposition of cations from the electrolyte on the surface of the anode exposed to the electrolyte

during charging.

  This feature acts to prevent the formation of dendrite which, in many cases, causes a failure

  of the element, since the covering of electropoly

  It can only take place inside the cavity structure of the support, which prevents it from becoming detached from the anode structure and / or causing internal short circuits. According to specific embodiments of the present invention when the carrier is a zeolite, the anode may be sodium sodalite, a mordenite in which suitable proportions of potassium and sodium have been absorbed, or a mordenite in which proportions have been absorbed

  suitable for potassium and lithium.

  In another specific embodiment of the invention, in which the material of the molecular sieve support is a nonconductive zeolite or a little electrically conductive zeolite it is possible to dispense with a separate liquid electrolyte and to have the molecular sieve support

  zeolite in direct and intimate contact with a cathode

  suitable solution such as absorbed sulfur in a graphite coated zeolite 4A. In this case, the sulfur (in the form of polysulfide) can act as an electrolyte and the zeolite in which the sulfur has been absorbed, can be considered as a catholyte. In this respect, the zeolite / sulfur catholyte is considered as a combined electrolyte / cathode assembly and the elements of the invention provide this possibility,

  with reference to an electrolyte and a cathode in context.

  to explain accordingly. If the zeolite material of the anode is too electronically conductive, to allow this, it may, however, be necessary to provide a

porous insulating layer between the support and the cathode,

  prégné a suitable liquid electrolyte. This porous insulating layer may consist of a suitable insulating, undoped dehydrated zeolite material. This embodiment has the advantage that, apart from the anode or source of electropositive material which will generally be in the molten state, the element will be substantially solid and

based on zeolite.

  In addition, when the element is operable at a sufficiently low temperature, it will be contemplated that clathrate molecular sieve carriers may be used in the same manner as previously mentioned mineral micromolecular sieve carriers. They should not be able, when used with aqueous electrolytes, for the same reasons, to absorb water, and should have a similar structure of the channel type and, similarly, the

  micromolecular sieve supports of a non-tectonic oxide

silicate can be used.

  The present invention will now be described by way of example.

  ples with reference to the accompanying diagrammatic drawings in which: Figure 1 shows a diagram of a device used as a conductive element for conductivity tests carried out on a zeolite support for an element according to the present invention; FIG. 2 represents a similar diagram of a test element according to the

  present invention and FIGS.

  feel the graphic results of the tests

  performed with the device of Figure 1.

  In Figures 1 and 2 of the drawings, the same references are used for the same parts, unless it is

otherwise specified.

  In FIG. 1, a conductive element generally designated by the reference numeral 10 comprises a pair of stainless steel cups 12 held together by circumferentially spaced insulating locking screws 14. In the cups 12 are contained alkaline metal electrodes at the same time. melt 16 and they are separated by a support 18 for an element according to the present invention. The support is fixed between the lips 12.1 of the cups 12 and acts to

  separate the electrodes 16 from each other.

  In Fig. 2 essentially the same arrangement is shown except that one of the electrodes 16 is replaced by a cathode / liquid electrolyte mixture so that the electrode 16 is an anode and the

  cups 12 act as current collectors.

  The present invention will be further described with reference to the following nonlimiting examples implemented with the

  device and the element of Figures 1 and 2.

EXAMPLE 1

  Referring to Figure 1, the carrier 18 was manufactured as a compact package or pellet containing zeolite 4A and kaolin. A mixture consisting of equal parts by weight of zeolite 4A and kaolin was milled by a ball mill for 24 hours and the pellet was pressed on a linear press at a pressure of 2 × 10 5 kPa. The pellet was baked at 650WC for 3 hours. After cooling, the shaped article was placed in a freshly prepared zeolite 4A gel in which the kaolin was converted to zeolite 4A and the pellet was further compacted by a counter-impregnation of zeolite 4A from the gel.

fresh. -

  Fully compacted pelletized object was released

  after 10 days, washed with distilled and dehydrated water

  Dried at 3600C and 10 kPa for 6 hours. The pellet was then subjected to a sodium metal impregnation in

  gaseous phase under vacuum at 350 ° C. for 2 to 3 hours.

  The charged pellet in which sodium is absorbed was then handled in a dry argon cuff box and the device of Fig. 1 was constructed and connected

  electrically to form a conductive element. This pro-

  cedure has been repeated a number of times and a number of such conductive elements have been constructed in

  also using potassium and lithium as dopant.

  The resistance R of the alternating current AC as a function of the temperature T was measured for the pellets. The typical pellet conductivity graph in the form of log aT (where a is the specific conductivity defined as = dR where d is the thickness of the pellet, A is the sectional area of the pellet and R is the resistor measured in ohms) as a function of temperature (103) is T

shown in Figure 3.

  The results of comparative tests are given in the following Table; Table 1 compares a tablet impregnated with sodium and pads impregnated with lithium and potassium, respectively

TABLE 1

  Metal (Tcm) 1 C Li 0.006 350 Na 0.050 350

K 0.010 350

EXAMPLE 2

  Other compact elements or pellets have been manufactured

containing a zeolite 4A.

  The pellets of Example 2 are then dehydrated and treated with sodium as described in Exemplel and

  tried at different temperatures.

  Figure 4 shows a typical graph of logaT based

  10- using the conductive element of Figure 1.

  T The test results are shown in the following Table (Table 2) for sodium

TABLE 2

(Pcm) -l ToC

0.006 200

0.020 250

0.060 300

EXAMPLE 3

  Small electrochemical test elements have been manufactured in accordance with FIG. 2, these elements comprising an alkali metal anode 16, a zeolite in which the pelletized alkali metal 18 is absorbed and a suitable compatible liquid electrolyte and a cathode 20. A test was carried out using a sodium anode, a sodium impregnated zeolite 4A as a pellet, and a potassium iodide / lithium iodide molten salt electrolyte mixed with the cathode material having zeolite crystals. 13X doped with sulfur absorbed and containing graphite for electronic conductivity. In this case, an open circuit voltage of 1.9V was obtained with a short circuit current of 35 mA with an effective surface

from about 1 cm2 to 3000C.

  Another cell was constructed using potassium for the anode, a zeolite 4A for the potassium impregnated pellet, a lithium aluminum chloride electrolyte

  and a zeolite 4A containing sulfur impregnated as cathode.

  In this case, an open circuit voltage of 2.0V was obtained with a short circuit current of 5 mA at a temperature of 2001C with an effective area of about 1 cm 2. Finally, an element was built in using a sodium anode, sodium impregnated in a zeolite support, an electrolyte of sodium aluminum chloride and as a sulfur cathode absorbed in a zeolite 4A. From this element, an open-circuit voltage of 1.9V was obtained with a short-circuit current of about 10 mA at 2000C with a surface

effective about 1 cm2.

  In all the above elements, the zeolite of the support was prepared by mixing it with kaolin as described.

in Example 1.

  All the elements described above fail at different times for reasons essentially not in

  electrochemistry, such as problems with

  dullness, breakage of the worked product, etc. It is hoped that routine experimentation will overcome these problems. Although some of these elements break down after a certain

  hours, others last up to about 7 days.

  An advantage of the present invention is that it provides an element in which the electrolyte is separated from the anode by a support which has a much higher amplitude conductivity than undoped tectosilicates, for example the zeolites described in FIG. Breck, Donald W. "Molecular sieves in zeolite" published by John Wiley and Sons, 1974

pages 397 to 410.

  It should be noted that the support tested, as it appears from FIGS. 3 and 4, has a conductivity which increases with the operating temperature, namely it has a positive temperature coefficient for the conductivity which indicates that the conductivity can be ionic or hybrid

  rather than purely metallic or electronic.

  As regards the construction in support of the present invention it is desired that it be completely liquid tight during use. For this reason, all necessary tests must be made to make it completely compact with no gaps, channels, etc. However, with regard to its operation, it should be noted that, after a period of stabilization or initial conditioning which may be necessary, there is in fact no change in the average chemical composition of the support during charging and discharging. and no change in the state

  oxidation of the electropositive substance.

Claims (17)

claims   1. An electrochemical element 10 having an anode 16 which comprises as electrochemically active anode material an electronically conductive electropositive substance which is in the molten state at the operating temperature of the element, a compatible electrolyte 20 and a compatible cathode 20 characterized in that it further comprises a sieve support   micromolecular 18 substantially non-electronically conductive   in which the electropositive substance is absorbed   and kept in dispersed form, the microsieve   molecular being liquid tight and placed between and separating the electrolyte and the cathode from the electropositive substance of the anode.   2. An element according to claim 1,   characterized in that the electrolyte is liquid at the time   operating temperature of the element and may react undesirably with the absorbed electropositive material and in which the carrier is selected or modified so that the windows in its microporous inward surface prevent sufficient inward access for 'a   such an adverse reaction takes place.   3. An element according to any one of claims 1   or 2, characterized in that the electropositive material of the anode is selected from the group consisting of alkali metals, alkaline earth metals, a combination or an alloy   of two or more alkali metals and / or alkaline   earth and a combination or alloy of one or more alkali metals and / or alkaline earth metals with one or more other substances.   4. An element according to claim 3, characterized in that the electropositive substance is (x <   sodium or an alloy of sodium and potassium.   5. An element according to any one of claims 1   at 4, characterized in that the support is a sieve support micromolecular mineral.   6. An element according to claim 5,   characterized in that the support is a tectosilicate.   7. An element according to claim 6, characterized in that the support is selected from the group consisting of zeolites, feldspars, feldsparents and silicates.   8. An element according to claim 7, characterized in that the electrolyte is an electrolyte to   base of molten salt and the support is a zeolite.   9. An element according to claim 7, characterized in that the electrolyte is an aqueous solution of a mineral salt and   in that the support is a feldspar or a feldspatholde.   An element according to any one of the claims 1 to 9,   characterized in that the cathode comprises as electrochemically active cathode material, a substance selected from the group consisting of oxides of one or more transition metals, hard metal compounds   intermediate-activated refractories and sulfur or selenium ab-   sorbed in the micromolecular sieve support.   An element according to any of the claims 1 to 10,   characterized in that the electrolyte is selected from the group consisting of aqueous solutions of bases, acids and   of mineral salts and by mineral salts in the molten state.   12. A composite anode structure 16, 18, characterized in that it comprises a micromolecular sieve support substantially non-electron-conducting 18 in which an electrochemically active anode material in the form of an electronically conductive electropositive substance is absorbed and maintained in dispersed form and a reservoir or source (16) of the electropositive material in contact with the support for use with a compatible electrolyte 20 and a cathode 20 in an electrochemical element 10 in which the electropositive substance of the reservoir is melted state and is separated by the support electrolyte.   An anode structure according to claim 12, characterized in that the electropositive anode substance is selected from the group consisting of alkali metals, alkaline earth metals, a combination or an alloy   of two or more alkali metals and / or alkaline   earth, and a combination or alloy of one or more alkali metals and / or alkaline earth metals with one or more several other substances.   An anode structure according to claim 13, characterized in that the electropositive substance is the   sodium or an alloy of sodium and potassium.   15. An anode structure according to any one of the claims   12 to 14, characterized in that the support is a sieve support micromolecular mineral.   An anode structure according to claim 15,   characterized in that the support is a tectosilicate.   17. An anode structure according to claim 16, 2 4 9 2 1 7 3   characterized in that the support is selected from the group consisting of zeolites, feldspars, feldspathoids and silicates.